The invention lies in the field of machining a workpiece according to a selected pattern by means of a focussed laser beam. Such an operation can for instance be the mutual connection of two metal plates over selected welding zones. A pattern of sandpaper pieces, for instance sanding discs, can also be cut from a strip of sandpaper which is for instance advanced continuously and which is unwound from a roll and wound onto a winding roll after processing. The operations can take place such that the target point of the focussed laser beam on the workpiece runs through a selected path. This path can be continuous or discontinuous. In the case of a discontinuous path, the laser is switched on and off respectively at the necessary moments. Focussing of the parallel, infrared laser beam takes place by means of a converging optical system.
For a proper understanding of the description of the invention following hereinbelow, two prior art examples are mentioned.
The first example relates to a welding operation using a laser, for instance a CO2-laser, with an output of 3000 W, operating area 1500×1500 mm, focal distance 2300 mm, welding speed about 20 mm/s. Due to the large focal distance there is a relatively large target point, whereby the weld is relatively wide, for instance in the order of 2 mm. A relatively large amount of heat is hereby introduced into the material for welding. If for instance a small piece has to be welded in each case on a car door in the four corners, this could be technically acceptable because the displacement times of the laser beam from the one corner to the next corner are negligibly small, i.e. in the order of 0.05 seconds.
A second example relates to the cutting of sandpaper using a laser output of 1500 W, an operating area of 750×750 mm, a focal distance of 1250 mm, a cutting speed of about 600 mm/s. At a material strip width of 1500 mm so-called scanners are for instance used adjacently of each other according to the prior art, which together cover the total material strip width. A scanner comprises a converging optical system for focussing the laser beam at a target point on the workpiece, with moving means for adjusting the spatial position and optionally the angular position of one or more components of the optical system such that the optical distance between this system and the target point of the focussed laser beam on the workpiece is substantially constant, and that the target point runs through a path corresponding with the selected machining pattern, all this under computer control. When sanding discs with a diameter of 125 mm are being cut from the sandpaper strip, the total output of both scanners is 12234 discs per hour.